8 Replies Latest reply on Mar 8, 2016 10:45 PM by alimac

    Static problems with cables to Analog Line In

    alimac

      Has anybody had any issues with awful static noises using a standard audio cable to the Analog Line In jack?  As long as the audio cable to the Line In is completely motionless the audio is okay, but if I touch it very lightly or move it in any way there is awful static.  I've tried different cables from different manufacturers (e.g. Monster) and different audio sources and the problem has persisted and if I go directly to a Bose speaker, there is no problem, so it isn't a bad cable with a short.  Can anyone tell me what's going on, or whether this is a known issue.  Could it be a problem with grounding?  Any help appreciated.  It's killing my project

        • Re: Static problems with cables to Analog Line In
          jw0752

          Hi Alistair,

          You can perhaps troubleshoot this problem a little further. Put the plug itself in an anchored situation like a small vise or a vise grip pliers so it can't move. With the board plugged in try moving the board to see if the static occurs. Next move the wire on the other side of the plug to see if the static is there. This should tell us if the problem is in the cord or in the connection of the plug to the jack on the board. It is not uncommon for the contact points in a jack to get oxidized and this produces a poor connection which can cause the static you mention. Also inspect the solder joints between the jack and the board for cracks or bad solder joints. If the problem is in the jack you might try a little old fashioned spray contact cleaner and plug the cable in and remove it several times. If the cable has an (RCA) Phono plug you can also try bending the outer fingers in so that they make a tighter fit to the jack. Let me know if this doesn't solve your problem. Incidentally a patch cord like this would show problems on an input where any static is amplified that you might not see when it is used on an output like for speakers. 

          John

            • Re: Static problems with cables to Analog Line In
              alimac

              Thank you John for the reply.  I'm using a standard 3.5mm audio cable to connect an iphone (ipod, etc) to the audio card.  The problem is definitely at the plug/jack interface on both ends of the cable.  Any movement of either 3.5mm plug in either the iphone/ipod or the audio card causes tremendous static noise.  I'm not sure why I can plug my iphone and same audio cable into a "Line In" in my car stereo, bose mini speaker, etc, and not have this problem, but it's a tremendous problem with the "Line in" for the RPi/audiocard.   Do you know what is different about this Line In or how I might be able to mitigate this?  I can look for a tighter fitting plug, but 3.5mm is 3.5mm..

               

              Thanks for your help.

               

              Alistair

                • Re: Static problems with cables to Analog Line In
                  jw0752

                  Hi Alistair,

                  Here is what I would try. Use a little 000 Steel wool and clean the tips of the 3.5 mm plugs. Spray a little contact cleaner on the tips and plug them in to see if this helps with the connections. It is possible that the type of input on the board makes it more sensitive than the car's input. Sometimes a little lubricant like that in the contact cleaner will help the metal stay in contact and not chatter when it move across the contact surfaces.

                  John

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                  • Re: Static problems with cables to Analog Line In
                    shabaz

                    Also, it may be worthwhile experimenting with resistors, just in case the ipod is doing something unexpected when it doesn't see a headphone load. I appreciate it seems fine with when you plug it into other devices though. It could be bursting some digital data or something bizarre in case the plugged in device was a headset with mic and volume controls etc. We just can't be sure since we don't know what the Apple design does (they are known to require unexpected (well, now expected from them ; ) things, such as using the proprietary accessory/charging port for a true line output).

                    I'd try putting (say) 47 ohm resistors from each of the channels (tip and ring) to the sleeve.

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